I use a vintage Suntour high normal front derailleur with my 52/42/24 and 11/32 (11/12/14/16/18/21/16/32) eight speed cassette.
I can't use the 24t chainring on the front while using the 11 or 12 cogs on the rear because the rear derailleur cage won't take up that much slack. But, those two gears are pretty cross chained so I do not use those gears. I also do not use the 52t front with the 26 or 32 because of cross chaining, but I made sure that I had enough chain so that if I accidentally shifted onto that, I would not bind anything up.
In other words, the rear and not the front is derailleur is the limiting factor.
Originally Posted by
Medic Zero
... ... I'm thinking something like 51-44-26, but the lower I can go while retaining the upper end would be best.
I think a 51 and 44 would be a huge error. My 52 and 42 are one and a half step gearing, meaning that a shift on the front is one and a half times larger than a shift of one cog on the rear. I have bought but have not yet installed a 46t to use instead of the 52t, that would be half step gearing so that a shift on the front is half as much as a shift of one cog on the rear. I plan to continue using one and a half step gearing around town but half step when loaded touring.
The advantage of half step or one and a half step gearing is that you can do fine tuning of your gearing. I frequently find that I am shifting down on one derailleur and up on the other for a very minor change in gearing for a minor change in windage or grade.
I think if you calculate gear inches for the 44t and 51t gears on your 11/32 cassette, you will find that almost every gear on 44t chainring has a duplicate gear with the 51t ring. The advantage of a 24 or 27 speed system is that you get a lot of gears but your plan for a 44t and 51t would give you several redundant gears, negating some of the advantages of a lot of gears.
The upshift from the 24t to the 42t is not a smooth shift, but it works. I do not know if you have a friction shifter for the front, you will probably need one.